A gas turbine device dedicated to low calorie gas combustion which is capable of using multiple types of low calorie gases with different calories at the same time is generally known as an example of a gas turbine device which uses a mixed gas obtained by mixing together three or more types of gases as a fuel gas for a combustor. The gas turbine device dedicated to low calorie gas combustion is used, for example, in a steel mill. In the steel mill, various excessive gases such as a blast furnace gas (B gas), a coke oven gas (C gas), and a converter gas (L gas) are produced in a manufacturing process of a steel product. These excessive gases contain combustible components. For this reason, the excessive gases are used as a fuel gas for the gas turbine device in the steel mill and the like, and thereby the excessive gases are effectively used.
There are large variations in amount of byproduct gases produced. For this reason, when used as the fuel for the gas turbine device, any of the excessive gases is not used singly, but a mixed gas obtained by mixing multiple types of gases is used. Moreover, calorie adjustment may be performed by further mixing a natural gas (LNG) and the like into the mixed gas.
For example, a gas turbine device disclosed in Patent Document 1 listed below is given as a specific example of the gas turbine device which uses the mixed gas of multiple types of excessive gases and the natural gas as the fuel gas for a combustor. In the gas turbine device disclosed in Patent Document 1, as shown in FIG. 4, the blast furnace gas, the coke oven gas, and the natural gas are mixed by a mixer 51, and this mixed gas is supplied to a combustor of a gas turbine 52 as the fuel gas.
In addition to Patent Document 1, Patent Document 2 is also given as a prior art document related to the present invention. Patent Document 2 discloses an example of a gas turbine device which reuses part of a combustion gas exhausted from a gas turbine by supplying the part of the combustion gas to an air compressor.    Patent Document 1: Japanese Patent Application Publication No. 2004-27975    Patent Document 2: Japanese Patent No. 2954456